Thermal oxidation of two grades of purified epoxidized natural rubber
(ENR 25 and ENR 50) and one grade of unmodified natural rubber (purifi
ed SMR L grade) were studied using Fourier Transform Infrared Spectros
copy (FTIR). Changes in the characteristic absorption band, particular
ly the hydroxyl and carbonyl peaks of the degraded rubbers are careful
ly monitored. Results indicate that thermal oxidation occurs in the do
uble bond region for SMR L to form oxidative products which mainly con
sist of hydroperoxide, hydroxyl and carbonyl compounds. In the case of
ENR, thermal oxidation occurs not only in the double bond region, but
also involves epoxide ring-opening reaction to yield oxidative produc
ts having similar functional groups as that of SMR L. For the three ru
bbers studied, increasing temperature of thermal oxidation increases t
he rate of oxidation. From a time-dependent study, it suggests that th
ermal oxidation of ENR is an autocatalytic process. No attempt, howeve
r, is made to ascertain the exact chemical structures of the oxidative
products formed in this study.